No association between CYP1A2 or CYP3A4 expression and blood glucose, TG or cholesterol levels in patients.Moderate/high risk obesity was significantly more frequent in low CYP3A4 expressers.In low CYP3A4 expressers, a significant correlation was found between clozapine serum concentration (or daily dose) and blood glucose level. The gene discussed is CYP1A2; the disease is obesity due to melanocortin 4 receptor deficiency.